Method of and apparatus for signal-waveform simulation, and computer product

ABSTRACT

The apparatus includes the wiring-model generation section that generates a wiring model in accordance with high-frequency-circuit design information; the random-pattern analysis section that generates and analyzes a dummy random-pattern waveform for transmitting a wiring model in accordance with a command including the bit information of a random-pattern waveform and a differential waveform corresponding to the dummy random-pattern waveform; and the skew analysis section that skews a random-pattern waveform or differential waveform in accordance with a preset skew width.

FIELD OF THE INVENTION

The present invention relates to a technology used for therandom-pattern analysis, skew analysis, jitter analysis, and eye-patternanalysis of differential signal or ordinary signal.

BACKGROUND OF THE INVENTION

Operation frequencies of information processing equipment such asnetwork units or personal computer have been remarkably raised recentlyfrom megahertz to gigahertz. Thereby, a waveform analysis consideringinfluences of various noises is requested also for a high-frequencysignal for transmitting a wiring pattern of a printed circuit board.

A circuit designer of an integrated circuit and the like selects acircuit device constituting a circuit and a parameter for controllingthe characteristic of the circuit device so that operations of thecircuit are suited to a purposed specification before designing thecircuit.

At the present when the computer art is developed, a circuit simulatoris used for circuit design. The circuit simulator simulates a circuitoperation on a computer without fabricating an actual circuit and showsthe circuit operation for a designer. The simulator operated by thesoftware referred to as SPICE2 developed by University of California atBerkley in 1972 is publicly known.

For example, in the case of an analysis using the above circuitsimulator, a simulation is executed in accordance with the connectiondata between circuit devices constituting a circuit to be analyzed anddevice parameters to estimate the number of noises under a predeterminedoperational state of each circuit device and display or print theestimated number of noises.

Moreover, a random-pattern analysis has been performed so far, in whichthe waveform of a random pattern is falsely generated to analyze thereflection characteristic when the random pattern is transmitted to thecircuit. As shown in FIG. 26A, the waveform of the random pattern showsa differential waveform constituted of a negative waveform 70 and apositive waveform 71.

Because the differential waveform makes it possible to cancel noises byusing the difference between the negative waveform 70 and positivewaveform 71 even if noises are superimposed on the negative waveform 70and positive waveform 71, it is a waveform having a high noisiness.Moreover, the differential waveform is defined as bit 0 when thepositive waveform 71 is equal to 0 V and bit 1 when the positivewaveform 71 is equal to 3 V.

The above random pattern is obtained by combining the bit 1 and the bit0 at random, in which the reflection characteristic is almost certainlydeteriorated in the case of a specific combination. Therefore, byintentionally falsely transmitting a random pattern to the circuit, itis possible to determine good or bad of the reflection characteristic.

To generate the waveform of a random pattern by a conventional circuitsimulator, it is necessary to carefully manually set rise and falltimings of the positive waveform 71 (Pos_Wave) and the negative waveform70 (Neg_Wave) as shown in FIG. 26B.

As described above, the conventional circuit simulator shows the powerin a waveform analysis up to approx. 100 MHz and is greatly supported byvarious designers. Because frequencies of information equipment havebeen remarkably raised recently and are reaching a gigahertz band from amegahertz band, a waveform analysis considering influences of variousnoises is requested for a high-frequency signal for transmitting awiring pattern to a printed circuit board.

However, the conventional circuit simulator has a problem that it is noteasy to correspond to signal analyses such as the skew analysis, jitteranalysis, and eye-pattern analysis of a high-frequency differentialsignal and a general signal.

Moreover, as described by referring to FIG. 26A and FIG. 26B, in thecase of the conventional circuit simulator, it is necessary to carefullymanually set rise and fall timings of the positive waveform 71 andnegative waveform 70. Therefore, the conventional circuit simulator hasproblems that the above operation is very troublesome and requires a lotof time and it is not easy to perform a random-pattern analysis.

SUMMARY OF THE INVENTION

It is an object of this invention to provide a method of and apparatusfor signal-waveform simulation using the random-pattern analysis, skewanalysis, jitter analysis, and the eye-pattern analysis ofhigh-frequency differential waveforms or ordinary signal waveforms. Itis another object of this invention to provide a computer readablerecording medium that stores a computer program which when executedrealizes the method according to the present invention.

The apparatus for signal-waveform simulation according to one aspect ofthis invention comprises a model generation unit which generates asignal-analysis simulation model in accordance withhigh-frequency-circuit design information; a random-pattern analysisunit which generates and analyzes a dummy random-pattern waveform fortransmitting the signal-analysis simulation model and a differentialwaveform corresponding to the dummy random-pattern waveform inaccordance with a command including the bit information of arandom-pattern waveform; and a skew analysis unit which skews therandom-pattern waveform or the differential waveform in accordance witha preset skew width.

The apparatus for signal-waveform simulation according to another aspectof this invention comprise a model generation unit which generates asignal-analysis simulation model in accordance withhigh-frequency-circuit design information; a random-pattern analysisunit which generates and analyzes a dummy random-pattern waveform fortransmitting the signal-analysis simulation model and a differentialwaveform corresponding to the dummy random-pattern waveform inaccordance with a command including the bit information of arandom-pattern waveform; and a setting unit which sets a region to beexcluded from a range to be analyzed in the random-pattern waveform orthe differential waveform.

The apparatus for signal-waveform simulation according to another aspectof this invention comprise a model generation unit which generates asignal-analysis simulation model in accordance withhigh-frequency-circuit design information; a random-pattern analysisunit which generates and analyzes a dummy random-pattern waveform fortransmitting the signal-analysis simulation model and a differentialwaveform corresponding to the dummy random-pattern waveform inaccordance with a command including the bit information of arandom-pattern waveform; and an eye-pattern analysis unit whichgenerates an eye-pattern waveform by superimposing waveforms obtained byframe-dividing the random-pattern waveform or the differential waveformby a division width that includes a waveform of one bit and is of onedata width or wider.

Other objects and features of this invention will become apparent fromthe following description with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing a configuration of an embodiment ofthe present invention;

FIG. 2 is an illustration showing a signal transmission circuit 20 inthe embodiment in FIG. 1;

FIG. 3 is a flowchart for explaining operations of the embodiment inFIG. 1;

FIG. 4A to FIG. 4D are illustrations for explaining a random-patterngeneration method in the embodiment in FIG. 1;

FIG. 5A and FIG. 5B are illustrations showing a random-pattern waveformin the embodiment in FIG. 1;

FIG. 6A to FIG. 6C are illustrations showing a random-pattern waveformin the embodiment in FIG. 1;

FIG. 7A and FIG. 7B are illustrations for explaining an skew analysis inthe embodiment in FIG. 1;

FIG. 8A and FIG. 8B are illustrations for explaining a skew analysis inthe embodiment in FIG. 1;

FIG. 9A and FIG. 9B are illustrations for explaining a command under ajitter analysis in the embodiment in FIG. 1;

FIG. 10A and FIG. 10B are illustrations for explaining a jitter analysisin the embodiment in FIG. 1;

FIG. 11A to FIG. 11C are illustrations for explaining a jitter analysisin the embodiment in FIG. 1;

FIG. 12A and FIG. 12B are illustrations for explaining an eye-patternanalysis in the embodiment in FIG. 1;

FIG. 13A to FIG. 13C are illustrations for explaining an eye-patternanalysis in the embodiment in FIG. 1;

FIG. 14A and FIG. 14B are illustrations showing an unstable region ofthe random-pattern waveform in the embodiment in FIG. 1;

FIG. 15A and FIG. 15B are illustrations showing an eye-pattern waveformcorresponding to the random-pattern waveform shown in FIG. 14A and FIG.14B;

FIG. 16A to FIG. 16C are illustrations for explaining anotherrandom-pattern waveform generation method in the embodiment in FIG. 1;

FIG. 17 is an illustration for explaining the case in which DUMMYEVENT=0in FIG. 16A;

FIG. 18A and FIG. 18B are illustrations showing a stable region of therandom-pattern waveform in the embodiment in FIG. 1;

FIG. 19A and FIG. 19B are illustrations showing an eye-pattern waveformcorresponding to the random-pattern waveform shown in FIG. 18A and FIG.18B;

FIG. 20A and FIG. 20B are illustrations showing an eye-pattern waveformobtained when the random-pattern waveform shown in FIG. 5 is distorted;

FIG. 21 is an illustration for explaining processing of frame-dividingin the embodiment in FIG. 1;

FIG. 22 is an illustration for explaining processing of frame-dividingin the embodiment in FIG. 1;

FIG. 23A and FIG. 23B are illustrations showing eye-pattern waveformsgenerated by the processing of frame-dividing in FIG. 21 and FIG. 22;

FIG. 24 is an illustration showing eye-pattern waveforms obtained byexecuting the processing of frame-dividing in FIG. 21 and FIG. 22 on therandom-pattern waveform shown in FIG. 18A and FIG. 18B;

FIG. 25 is a block diagram showing a modification of the embodiment inFIG. 1; and

FIG. 26A and FIG. 26B are illustrations for explaining a conventionalrandom-pattern waveform generation method.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiment/s of a method of and apparatus for signal-waveformsimulation, and a computer product according to the present inventionis/are described below in detail by referring to the accompanyingdrawings.

FIG. 1 is a block diagram showing an embodiment of the presentinvention. FIG. 1 shows, for example, a configuration of asignal-waveform simulation apparatus to be applied tohigh-frequency-circuit design. The signal-waveform simulation apparatusis an apparatus for executing the random-pattern analysis, eye-patternanalysis, jitter analysis, and skew analysis of a high-frequency signalfor transmitting a circuit to be designed (e.g. printed board circuit).

The input section 1 is used to input the wiring data, the parameter, andvarious commands of a circuit to be designed. FIG. 2 is an illustrationshowing a signal transmission circuit 20 as an example of the abovecircuit. The signal transmission circuit 20 shown in FIG. 2 serves as acircuit capable of performing bidirectional signal transfer betweentransceiving circuits 30 and 50 through a printed wiring 40(transmission line).

In the printed wiring 40, a superimposed signal between a transmittersignal DS₁ transmitted from a driver 31 and a transmitter signal DS₂transmitted from a driver 51 is transmitted. The characteristicimpedance of the printed wiring 40 is assumed as Z₀. In the transceivingcircuit 30, the driver 31 serves as a circuit for transmitting thetransmitter signal DS₁ to the transceiving circuit 50 through theprinted wiring 40.

The output resistance of the driver 31 is assumed as an outputresistance R_(out1). A correction circuit 33 outputs the transmittersignal DS₁ to a receiver 32 as a correction signal. The receiver 32receives the transmitter signal DS₂ as a receiver signal DR₂ byobtaining the difference between the superimposed signal (transmittersignal DS₁+transmitter signal DS₂) sent from the printed wiring 40 andthe correction signal (transmitter signal DS₁) generated by thecorrection circuit 33.

In the transceiving circuit 50, the driver 51 serves as a circuit fortransmitting the transmitter signal DS₂ to the transceiving circuit 30through the printed wiring 40. The output resistance of the driver 51 isassumed as an output resistance R_(out2). A correction circuit 53outputs the transmitter signal DS₂ to a receiver 52 as a correctionsignal. The receiver 52 receives the transmitter signal DS₁ as areceiver signal DR₁ by obtaining the difference between the superimposedsignal (transmitter signal DS₁+transmitter signal DS₂) sent from theprinted wiring 40 and the correction signal (transmitter signal DS₂)generated by the correction circuit 53. Moreover, in the case of thesignal transmission circuit 20, it is necessary to match thecharacteristic impedance Z₀ with the output resistance R_(out1) (outputresistance R_(out2)) in order to prevent reflection of a signal.

In FIG. 1, a control section 2 controls various sections and mainlyperforms the control for signal analysis. Details of operations of thecontrol section 2 will be described later. A storage section 3 storeswiring data and parameters. A wiring-model generation section 4generates a wiring model for signal analysis in accordance with theabove wiring data.

A random-pattern analysis section 5 performs a random-pattern analysisin accordance with a signal of a bit string comprising a randomcombination between 0 and 1 referred to as a random pattern (refer toFIG. 5A and FIG. 5B). An eye-pattern analysis section 6 generates an eyepattern (refer to FIG. 12A and FIG. 12B) by superimposing randompatterns every data width (UI: Unit Interval) to analyze the eyepattern.

A jitter analysis section 7 performs a jitter analysis of falselygenerating jitter (refer to FIG. 10B) in a random-pattern waveformcomprising the negative waveform 70 and positive waveform 71 shown inFIG. 10A. A skew analysis section 8 performs a skew analysis of falselygenerating a skew (phase difference) between the negative waveform 70and positive waveform 71 shown in FIG. 7A and FIG. 8A. A determinationsection 9 determines whether a differential waveform and an eye patternmeet predetermined criteria. A display section 10 is a display fordisplaying a series of analysis results above described. A bus 11connects various sections of the apparatus.

Operations of the above embodiment are described by referring to theflowchart shown in FIG. 3. In step SA1, a wiring pattern for a circuitto be simulated is designed. A parameter corresponding to the wiringpattern is input from the input section 1. In this case, the followingparameters used for various types of determinations to be describedlater are also input from the input section 1.

-   VIDMX: MAX (maximum value) of Magnitude differential Input Voltage    (|VID|) (Refer to FIG. 6C.)

Unit: [V] that can be designated up to the third decimal place.

-   VIDMN: MIN (minimum value) of Magnitude differential Input Voltage    (|VID|) (Refer to FIG. 6C.)

Unit: [V] that can be designated up to the third decimal place.

-   |VID|_WD: Differential voltage amplitude |VID| determination time    interval showing what-percent time interval of one data width (UI:    Unit Interval) of a random pattern (Refer to FIG. 6C.)

Unit: [%] that can be designated up to the third decimal place

-   VICMX: Common mode Input Voltage (VIC: MAX (maximum value) of common    mode voltage amplitude) (Refer to FIG. 6A.)

Unit: [V] that can be designated up to the third decimal place

-   VICMN: MIN (minimum value) of Common mode Input Voltage (VIC) (Refer    to FIG. 6A.)

Unit: [V] that can be designated up to the third decimal place

-   EYEXA: MIN (minimum value) of X-axis Eye Diagram Mask EYEXA (Refer    to FIG. 13A.)

Unit: [ps] that is designated by an integer

-   EYEXB: MIN (minimum value) of X-axis Eye Diagram Mask EYEXB (Refer    to FIG. 13A.)

Unit: [Ps] that is designated by an integer

-   EYEYA: MIN (minimum value) of Y-axis Eye Diagram Mask EYEYA (Refer    to FIG. 13A.)

Unit: [V] that can be designated up to the third decimal place

The control section 2 stores the parameters in the storage section 3 andsimultaneously starts the wiring-model generation section 4. In stepSA2, the wiring-model generation section 4 executes the wiring modelingfor modeling a wiring pattern in accordance with the above parameters.In step SA3, the processing for generating the above random pattern isexecuted. Specifically, a user inputs a random-pattern generationcommand 60 having the format shown in FIG. 4A. The random-patterngeneration command 60 is a command for generating the random-patternwaveform shown in FIG. 5A corresponding to the random bit string 63shown in FIG. 4D.

In the random-pattern generation command 60, EYEBIT (Input Bit Pattern)is used to set a random bit (random combination between 0 and 1)corresponding to a random-pattern waveform. In the case of theembodiment, [Input Bit Pattern] and the random-bit-pattern format 61shown in FIG. 4B are prepared so as to be easily designated by a user.

BITWIDTH [Bit-Width] sets one bit width of the random bit string 63shown in FIG. 4D. EYEEVENT [Eye-pattern Event] sets the number ofrepetitions of a bit pattern set in accordance with EYEBIT [Input BitPattern]. FIG. 4C illustrates a setting example of a random-patterngeneration command 62.

Moreover, when the random-pattern generation command 62 is input, therandom-pattern analysis section 5 generates a random-pattern waveformconstituted of the positive waveform 71 and negative waveform 70 shownin FIG. 5A and the differential waveform 72 shown in FIG. 5B in stepSA4. The random-pattern waveform and differential waveform 72 correspondto random-pattern bits. The differential waveform 72 is a waveformobtained by using the difference between the positive waveform 71 andnegative waveform 70 (positive waveform 71-negative waveform 70). Theanalysis result of the random pattern is displayed on the displaysection 10 in step SA11 to be described later.

In step SA5, the control section 2 determines whether a skew analysiscommand is input from the input section 1. When the determination resultis “No”, the control section 2 performs the determination in step SA7.However, when the determination result in step SA5 is “Yes”, the controlsection 2 starts the skew analysis section 8. Thereby, in step SA6, theskew analysis section 8 executes the processing of skewing the positivewaveform 71 or negative waveform 70 in the random-pattern waveform shownin FIG. 5A.

To skew the positive waveform 71, a user sets rise and fall timings ofthe positive waveform 71 (Pos_Wave) and negative waveform 70 (Neg_Wave)as shown in FIG. 7B. In this case, as shown in FIG. 7A, the timings areset so that the phase of the positive waveform 71 (Pos_Wave) delays fromthat of the negative waveform 70 (Neg_Wave) by 100 ps (Skew_Max).

However, to skew a negative waveform 70, the user sets rise and falltimings of the positive waveform 71 (Pos_Wave) and negative waveform 70(Neg_Wave) as shown in FIG. 8B. In this case, as shown in FIG. 8A, thetimings are set so that the phase of the negative waveform 70 (Neg_Wave)delays from that of the positive waveform 71 (Pos_Wave) by 100 ps(Skew_Max). The skew analysis results are displayed on the displaysection 10 in step SA11 to be described later.

In step SA7, the control section 2 determines whether a jitter additioncommand (refer to FIG. 9) is input from the input section 1. When thedetermination result is “No”, the control section 2 performs thedetermination in step SA9. However, when the determination result instep SA7 is “Yes”, the control section 2 starts the jitter analysissection 7. Thereby, in step SA8, the jitter analysis section 7 executesthe jitter analysis of generating jitter in the positive waveform 71 andnegative waveform 70 in the random-pattern waveforms shown in FIG. 10Aand FIG. 10B.

In this case, the jitter addition command 80 shown in FIG. 9A is inputby a user. In the jitter addition command 80, ADDJITTER [Jitter_Value]designates a jitter value (ps) to be added to the negative waveform 70and positive waveform 71 shown in FIG. 10A, which corresponds to the JV(jitter addition value) shown in FIG. 10B. FIG. 9B illustrates a jitteraddition command 81 as a designation example.

Moreover, the jitter analysis section 7 causes jitter by executing thejitter addition command 80 and swinging the negative waveform 70 andpositive waveform 71 rightward and leftward by the jitter addition valueJV (total of 2 JV) as shown in FIG. 10B. The jitter analysis result isdisplayed on the display section 10 in step SA11 to be described later.In this case, the jitter analysis section 7 also displays a bold line 90in order to make a portion where jitter occurs clear as shown in FIG.10B.

Moreover, FIG. 11A to FIG. 11C illustrate the jitter analysis of anotherwaveform. In this case, the jitter analysis section 7 swings thewaveform 100 shown in FIG. 11A rightward and leftward by a predeterminedjitter addition value JV as shown in FIG. 11B. A waveform 101 is awaveform when the waveform 100 is maximally swung leftward and awaveform 102 is a waveform when the waveform 100 is maximally swungrightward. In this case, the jitter analysis section 7 also displays anenvelope 103 shown by a bold line in order to make a portion wherejitter occurs clear as shown in FIG. 11C.

In step SA9, the control section 2 determines whether an eye-patternanalysis command is input from the input section 1. When thedetermination result is “No”, the control section 2 executes theprocessing in step SA10. However, when the determination result in stepSA9 is “Yes”, the control section 2 starts the determination section 9.Thereby, the determination section 9 determines good or bad of an eyepattern from step SA12 to step SA14.

Good or bad is determined for the following three cases.

-   (Case 1) Eye-pattern analysis of a random-pattern waveform to which    skew analysis is not applied-   (Case 2) Eye-pattern analysis of a random-pattern waveform in which    the positive waveform 71 delays from the negative waveform 70 by    Skew_MAX as shown in FIG. 7A-   (Case 3) Eye-pattern analysis of a random-pattern waveform in which    the negative waveform 70 delays from the positive waveform 71 by    Skew_MAX as shown in FIG. 8A

Moreover, in the case of the good/bad determination of an eye pattern,cases are also determined in which a jitter analysis is applied torandom-pattern waveforms of the above (case 1) to (case 3).

In step SA12, the eye-pattern analysis section 6 executes the processingof frame-dividing a waveform by one data width (UI_(—)1, UI_(—)2, . . ., UI_n) as shown in FIG. 12A. In step SA13, the eye-pattern analysissection 6 superimposes the frame-divided waveforms as shown in FIG. 12Band FIG. 13B to display an eye-pattern waveform on the display section10.

The eye-pattern waveform 110 shown in FIG. 12B is obtained bysuperimposing the frame-divided differential waveforms 72 shown in FIG.12A. The eye-pattern waveform 130 shown in FIG. 13B is obtained bysuperimposing the frame-divided random-pattern waveforms (negativewaveform 70 and positive waveform 71) shown in FIG. 12A.

In step SA14, the determination section 9 determines qualities of theeye-pattern waveforms 130 and 110 shown in FIG. 13B and FIG. 13C inaccordance with the reference eye pattern 120 shown in FIG. 13A. Theseeye-pattern waveforms 130 and 110 are better as a determination resultas the area of an eye (inner portion) increases.

Specifically, when the eye portion of the eye-pattern waveform 130 or110 even slightly enters the reference eye pattern 120, thedetermination section 9 sets the determination result to “bad”. In thiscase, the determination section 9 displays waveforms corresponding to anerror bit and two bits before and after the error bit among thoseconstituting the eye-pattern waveform 130 or 110.

Moreover, when the eye portion of the eye-pattern waveform 130 or 110does not enter the reference eye pattern 120, the determination section9 sets the determination result to “good”. In step SA11, the aboveanalysis results are displayed on the display section 10.

However, when the determination result in step SA9 is “No”, thedetermination section 9 performs good/bad determinations of therandom-pattern waveform shown in FIG. 5A and the differential waveform72 shown in FIG. 5B in step SA10. Good/bad determination is performedfor the following three cases.

-   (Case 1) Good/bad determination when a skew analysis is not    performed-   (Case 2) Good/bad determination when the positive waveform 71 delays    from the negative waveform 70 by Skew_MAX as shown in FIG. 7A-   (Case 3) Good/bad determination when the negative waveform 70 delays    from the positive waveform 71 by Skew_MAX as shown in FIG. 8A

Moreover, for the embodiment, cases are good/bad-determined in which ajitter analysis is applied to random-pattern waveforms of the above(Case 1) to (Case 3).

Specifically, the determination section 9 determines whether the valueof (((value of positive waveform 71)+(value of negative waveform 70))/2)shown in FIG. 5A (hereafter referred to as VIC (common code voltageamplitude)) is kept in a preset VIC range (VICMN to VICMX). When VIC iskept in the VIC range, the good/bad determination result is assumed as“good”. When VIC is not kept in the VIC range, the good/baddetermination result is assumed as “bad”.

The determination section 9 determines whether the differential voltageamplitude |VID| ((value of positive waveform 71)−(value of negativewaveform 70)) shown in FIG. 5B is kept in the reference range 73 shownin FIG. 6C, that is, between VIDMN and VIDMX in the whole |VID|_WD. When|VID| is kept in the reference range 73, the good/bad determinationresult is assumed as “good”. When |VID| is not kept in the referencerange 73, the good/bad determination result is assumed as “bad”.

In step SA11, the random-pattern waveform and the differential waveform72 shown in FIG. 6A and FIG. 6B are displayed on the display section 10and the good/bad determination result in step SA10 is displayed.

An example is described above in which goodness or badness of theeye-pattern is determined according to the random-pattern waveformconstituted of the positive waveform 71 and negative waveform 70 (referto FIG. 5A), and the differential waveform 72 (refer to FIG. 5B), whichare generated by the random-pattern generation command 62.

In other words, by the random-pattern generation command 62 shown inFIG. 4C, the random-pattern waveform and differential waveform in whicha bit pattern “1011011100” (EYEBIT) is repeated five hundred times(EYEEVENT), are generated.

When a capacitance component of a coupling capacitor is included forexample in the printed wiring 40 (transmission line) shown in FIG. 2, asa transient phenomenon, unstable regions in the random-pattern waveformand differential waveform as shown in FIG. 14A and 14B may be generated.The unstable regions are often generated at the initial stage of theabove-explained repetitions of the bit pattern, and have adverse effectson the eye-pattern determination.

The adverse effects on the eye-pattern determination caused by theunstable regions will be explained below. FIG. 14A shows arandom-pattern waveform constituted of a negative waveform 140 andpositive waveform 141 at an initial stage of the repetitions. Theinitial stage referred to here means a transition period T (from time t0to time t1) during the first to third repetitions. The random-patternwaveform becomes stable at and after time t1.

Thus in the transition period T, there is a bit pattern of 30 bits (onedata width equivalent to UI_(—)1-UI_n) constituted of “1011011100”(first repetition), “1011011100” (second repetition) and “1011011100”(third repetition).

In contrast to the random-pattern waveform in the stable region shown inFIG. 5A, the random-pattern waveform shown in FIG. 14A obviously has anunstable amplitude and is distorted and unsuitable for eye-patterndetermination.

A differential waveform 142 shown in FIG. 14B is a waveform obtained byusing the difference between the positive waveform 141 and negativewaveform 140 (positive waveform 141—negative waveform 140). Thedifferential waveform 142, like the random-pattern waveform (refer toFIG. 14A), obviously has an unstable amplitude and is distorted andunsuitable for eye-pattern determination, in contrast to thedifferential waveform in the stable region shown in FIG. 5B.

To perform the eye-pattern determination, in step SA12 shown in FIG. 3,the eye-pattern analysis section 6 executes the processing offrame-dividing the random-pattern waveform (refer to FIG. 14A) and thedifferential waveform (refer to FIG. 14B) by one data width (UI_(—)1,UI_(—)2, . . . , UI_n)

In step SA13, the eye-pattern analysis section 6 superimposes theframe-divided random-pattern waveforms and differential waveforms asshown in FIG. 15A and FIG. 15B to display eye-pattern waveforms 143 and144 on the display section 10.

The eye-pattern waveform 143 shown in FIG. 15A is obtained bysuperimposing the frame-divided random-pattern waveforms (the negativewaveform 140 and positive waveform 141) shown in FIG. 14A. Theeye-pattern waveform 144 shown in FIG. 15B is obtained by superimposingthe frame-divided differential waveforms 142 shown in FIG. 14B.

Since the “eyes” in the eye-pattern waveforms 143 and 144 are squashed,the above mentioned accurate good/bad determination of the eye-patterncannot be performed.

Thus in the embodiment, a setting is carried out, in which the unstableregions (transition period T: refer to FIGS. 14A and 14B) in therandom-pattern waveform and differential waveform are excluded from theranges to be determined and displayed.

Specifically, in step SA3 shown in FIG. 3, the user inputs arandom-pattern generation command 150 of the format shown in FIG. 16A.The random-pattern generation command 150 is a command for generatingthe random-pattern waveform corresponding to a random bit string.

In the random-pattern generation command 150, EYEBIT [Input BitPattern], BITWIDTH [Bit-Width] and EYEEVENT [Eye-pattern Event] areequivalent to those in the random-pattern generation command 60 (referto FIG. 4A).

In other words, in the random-pattern generation command 150, EYEBIT[Input Bit Pattern] is used to set a random bit (random combinationbetween 0 and 1) corresponding to the random-pattern waveform. In theembodiment, [Input Bit Pattern], and a random-bit-pattern format 151shown in FIG. 16B are prepared so as to be easily designated by a user.

BITWIDTH [Bit-Width] sets a bit width of the random bit string. EYEEVENT[Eye-pattern Event] sets number of repetitions of the bit pattern set inaccordance with EYEBIT [Input Bit Pattern].

DUMMYEVENT [Dummy Event] sets period of non-displaying therandom-pattern waveform and the differential waveform and not performingeye-pattern determination, by the number of repetitions of the bitpattern. During the period set in accordance with DUMMYEVENT [DummyEvent] a waveform analysis is performed as the internal processing. Asetting example of a random-pattern generation command 152 is shown inFIG. 16C.

In the random-pattern generation command 152, a random-pattern 153(random-pattern waveform and differential waveform) in which a bitpattern, “1011011100” (EYEBIT) with a bit width (BITWIDTH) ofone-thousand-two-hundred-and-fifty, is repeated one-hundred-and-threetimes (DUMMYEVENT+EYEEVENT).

As for the random-pattern 153, the random-pattern waveform anddifferential waveform of the random-pattern having a number of events ofthree (from first to third repetitions; referred to as a dummy eventbelow) are not displayed on the display section 10 (refer to FIG. 1),and eye-pattern determination is not performed.

As for the case of the random-pattern after the dummy event, having anumber of events of one hundred (from fourth to one-hundred-thirdrepetitions), the random-pattern waveform and differential waveform aredisplayed on the display section 10 and eye-pattern determination isperformed.

When the random-pattern generation command 152 is input, therandom-pattern analysis section 5 generates a random-pattern waveformand differential waveform corresponding to the random-pattern 153 (referto FIG. 16C) in step SA4 shown in FIG. 3. Therefore, the random-patternwaveform and differential waveform generated have unstable regions (fromfirst to third repetitions) and stable regions (from fourth toone-hundred-third repetitions).

The results of the random-pattern analysis are displayed on the displaysection 10 in a later-described step SA11. The display section 10displays the random-pattern waveform and differential waveform of thestable regions (refer to FIGS. 18A and 18B) excluding theabove-mentioned unstable regions (refer to FIGS. 14A and 14B).

FIG. 18A shows a random-pattern waveform constituted of a negativewaveform 160 and positive waveform 161 beyond the third repetition. Therandom-pattern waveform obviously has a stable amplitude and a regularwaveform in contrast to the random-pattern waveform of the unstableregion shown in FIG. 14A.

FIG. 18B shows a differential waveform 162 obtained by using thedifference between the positive waveform 161 and negative waveform 160(positive waveform 161—negative waveform 160) shown in FIG. 18A. Thedifferential waveform 162 also has a stable amplitude and a regularwaveform like the random-pattern waveform (refer to FIG. 18A).

To perform eye-pattern determination, the eye-pattern analysis section 6executes the processing of frame-dividing the random-pattern waveform(refer to FIG. 18A) and differential waveform (refer to FIG. 18B) by onedata width (UI_n+1, . . . ), in step SA12 shown in FIG. 3.

In step SA13, the eye-pattern analysis section 6 superimposes theframe-divided waveforms as shown in FIG. 19A and FIG. 19B to displayeye-pattern waveforms on the display section 10.

The eye-pattern waveform 163 shown in FIG. 19A is obtained bysuperimposing the frame-divided random-pattern waveforms (negativewaveform 160 and positive waveform 161) shown in FIG. 18A. Theeye-pattern waveform 164 shown in FIG. 19B is obtained by superimposingthe frame-divided differential waveforms 162 shown in FIG. 18B.

In the eye-pattern waveforms 163 and 164, it is obvious that “eyes” areclear and eye-pattern determination can be performed, in contrast to theeye-pattern waveforms 143 and 144 shown in FIGS. 15A and 15B.

In step SA14, the determination section 9, as explained above,determines good or bad of the eye-pattern waveforms 163 and 164 shown inFIGS. 19A and 19B according to the reference eye-pattern 120 shown inFIG. 13A. The above-described operations are executed after that.

When a setting of DUMMYEVENT=0 is used in FIG. 16A, display andeye-pattern waveform determination of the random-pattern waveform anddifferential waveform corresponding to bit patterns of all repetitionsincluding the first repetition are performed. FIG. 17 shows a settingexample of a random-pattern generation command 154 in whichDUMMYEVENT=0.

By the random-pattern generation command 154, a random-pattern 155(random-pattern waveform and differential waveform) in which a bitpattern “1011011100” (EYEBIT) having a bit width (BITWIDTH) ofone-thousand-two-hundred-and-fifty is repeated one-hundred times(EYEEVENT), is generated.

In the random-pattern 155, there is no dummy event, the random-patternwaveform and differential waveform corresponding to the random-patternhaving a number of events of one hundred (one to hundred repetitions)are displayed on the display section 10 and eye-pattern determination isexecuted.

In the above-mentioned embodiment, an example, in which the waveform isframe-divided by one data width (UI_(—)1, UI_(—)2, . . . , UI_n) uponprocessing of frame-dividing of step SA12 (refer to FIG. 3) as shown inFIG. 12A, is described. The dividing origin in the frame-dividing is across-point of the negative waveform 70 and positive waveform 71.

When transmission line characteristics of the printed wiring 40(transmission line) shown in FIG. 2 are debased, phase shifts anddistortion in the random-pattern waveform and differential waveform mayoccur. Eye-pattern waveforms generated using the random-pattern waveformand differential waveform in which such phase shifts and distortionoccur have their “eyes” shifted away from the center positions orchipped as shown in FIG. 20A and 20B. Therefore, in this case, good/baddetermination of the eye-patterns cannot be performed.

The eye-pattern waveform 170 shown in FIG. 20A corresponds to therandom-pattern waveform. The eye-pattern waveform 171 shown in FIG. 20Bcorresponds to the differential waveform.

When such a problem arises, as shown in FIG. 21 and FIG. 22, eye-patternwaveforms of which their good or bad can be determined are generated byframe-dividing the waveforms by a width that is wider than one datawidth UI.

Specifically, in step SA12 shown in FIG. 3, the eye-pattern analysissection 6 executes the processing of frame-dividing a random-patternwaveform, constituted of a positive waveform 180 and negative waveform181, and a differential waveform 182, shown in FIG. 21, by a dividingwidth (F1, F2, . . . , Fn) that is twice the width of one data width.

For example, in the case of the dividing width F2, the eye-patternanalysis section 6 firstly shifts a dividing origin Pa (cross point ofthe positive waveform 180 and negative waveform 181) half of one datawidth UI/2 to the left to set a new dividing origin Pa′ there. Thedividing origin Pa is equivalent to the dividing origin of FIG. 12A.

Secondly, the eye-pattern analysis section 6 sets the dividing width F2having a width that is twice the width of one data width UI from the newdividing origin Pa′. In this setting, adverse effects of phase shiftsand distortion on the eye-pattern waveform are absorbed because thedividing width F2 is wider than one data width UI_(—)2 that correspondsto one bit worth of random-pattern waveform and differential waveform182. Other dividing widths F1, and F3-Fn can be set in the same manneras that of the dividing width F2 described above.

In step SA13, the eye-pattern analysis section 6 superimposes waveformsframe-divided respectively by the dividing width F1-Fn, and displayseye-pattern waveforms 193 and 194 shown in FIG. 23A and FIG. 23B, on thedisplay section 10. The eye-pattern waveforms 193 and 194 shown in FIG.23A and FIG. 23B have a width that is twice the width of one data widthUI (2UI). The “eyes” corresponding to one-data-width UI portion of thewidth 2UI are clear and good or bad of the eye-patterns can then bedetermined for these waveforms. The good/bad determination of theeye-patterns is performed in accordance with the operations describedabove.

Left side section of a random-pattern waveform constituted of a negativewaveform 190 and positive waveform 191 and left side section of adifferential waveform 192, which are shown in FIG. 22, can beframe-divided in accordance with the above-described dividing method bythe dividing width (F1, F2, . . . , Fn) that is twice the width of onedata width, as shown in FIG. 22, in step SA12 shown in FIG. 3.

For example, in the case of the dividing width F6 shown in FIG. 22, theeye-pattern analysis section 6 firstly shifts a dividing origin Pb(cross-point of the negative waveform 190 and positive waveform 191)half of one data width UI/2 to the left to set a new dividing originPb′.

Secondly, the eye-pattern analysis section 6 sets the dividing width F6having a width that is twice the width of one data width UI from the newdividing origin Pb′. In this setting, adverse effects of phase shiftsand distortion on the eye-pattern waveforms are absorbed because thedividing width F6 is wider than one data width UI_(—)6 that correspondsto one bit worth of the random-pattern waveform and differentialwaveform 192. Other dividing widths F1-F5, and Fn can be set in the samemanner as that of the dividing width F6 described above.

In step SA13, the eye-pattern analysis section 6 superimposes waveformsframe-divided respectively by the dividing width F1-Fn, and displayseye-pattern waveforms 193 and 194 shown in FIG. 23A and FIG. 23B, on thedisplay section 10. The eye-patterns in this case also have “eyes” thatare clear and good or bad of the eye-patterns can then be determined forthese waveforms. The good/bad determination of the eye-patterns isperformed in accordance with the operations described above.

Eye-pattern waveforms 195 and 196 shown in FIG. 24 are generated whenthe processing of dividing according to FIG. 21 and FIG. 22 is executedfor the random-pattern waveform and differential waveform 162 shown inFIG. 18A and FIG. 18B. The eye-pattern waveforms 195 and 196 in FIG. 24also have a data width that is twice the width of one data width UI(2UI). The “eyes” corresponding to one-data-width UI portion of thewidth 2UI are clear and good or bad of the eye-patterns can then bedetermined for these waveforms.

Goodness or badness of the eye-pattern waveform corresponding to one ofthe random-pattern waveform and the differential waveform can bedetermined selectively.

As described above, according to the above-explained embodiment, awiring model is generated in accordance with the parameter (designinformation) about a high-frequency circuit and a dummy random-patternwaveform for transmitting a wiring model and a differential waveformcorresponding to the dummy random-pattern waveform are generated to skewthe random-pattern waveform or differential waveform in accordance witha preset skew width (Skew_MAX). Therefore, it is possible to easilyperform the random-pattern analysis and skew analysis of high-frequencydifferential waveforms or ordinary signal waveforms.

Moreover, jitter is caused in a random-pattern waveform in accordancewith a preset jitter addition value (JV) and an eye-pattern waveform isgenerated by superimposing frame-divided random-pattern waveforms ordifferential waveforms. Therefore, it is possible to easily perform thejitter analysis and eye-pattern analysis of high-frequency differentialwaveforms or ordinary signal waveforms.

Furthermore, good/bad determination of a differential waveform oreye-pattern waveform is performed in accordance with a preset referencevalue as described in steps SA10 and SA14. Therefore, it is possible toimmediately return a good/bad determination result to high-frequencycircuit design.

Moreover, a signal-analysis simulation model is generated in accordancewith high-frequency-circuit design information; a dummy random-patternwaveform for transmitting the signal-analysis simulation model and adifferential waveform corresponding to the dummy random-pattern waveformare generated in accordance with a command including the bit informationof a random-pattern waveform; and region to be excluded (for example, aregion that would have adverse effects on the analysis) from a range tobe analyzed when analyzing the random-pattern waveform or differentialwaveform, is set in the DUMMYEVENT shown in FIG. 16C. As a result,accuracy of the analysis can be increased.

Furthermore, good or bad of an eye-pattern waveform corresponding to therandom-pattern waveform or differential waveform in accordance with apreset reference value, over the range excluding the region (forexample, the region of which good or bad of the eye-pattern can bedetermined) set in DUMMYEVENT, is determined. Thus, accuracy of thegood/bad determination of the eye-pattern can be increased.

Moreover, as already explained in reference to FIG. 21 and FIG. 22, aneye-pattern waveform is generated by superimposing waveforms obtained byframe-dividing the random-pattern waveform or differential waveform by adivision width that includes one bit worth of waveform and is of onedata width UI or wider (twice the width of one data width UI).Therefore, effects of phase shifts and distortion are decreased, theeye-pattern waveform of which good or bad can be determined is generatedand accuracy of the good/bad determination can be increased.

An embodiment of the present invention is described above by referringto the accompanying drawings. However, a specific configuration is notrestricted to the embodiment. Design modifications are also included inthe present invention as long as they are not deviated from the gist ofthe present invention. For example, in the case of the above embodiment,it is also permitted to realize functions of the signal-waveformsimulation apparatus shown in FIG. 1 by recording a signal-waveformsimulation program for realizing functions of the signal-waveformsimulation apparatus in the computer-readable recording medium 300 shownin FIG. 25 and making the computer 200 shown in FIG. 25 read and executethe signal-waveform simulation program recorded in the recording medium300.

The computer 200 shown in FIG. 25 is constituted of a CPU 201 forexecuting the above signal-waveform simulation program, an input unit202 including a keyboard and a mouse, a ROM (Read Only Memory) 203 forstoring various data values, a RAM (Random Access Memory) 204 forstoring operation parameters, a reader 205 for reading a signal-waveformsimulation program from a recording medium 300, an output unit 206including a display and a printer, and a bus BU for connecting varioussections of the apparatus.

The CPU 201 realizes functions of the above signal-waveform simulationapparatus by reading a signal-waveform simulation program from therecording medium 300 via the reader 205 and then executing thesignal-waveform simulation program. The recording medium 300 includesnot only a portable recording media such as an optical disk, a floppydisk, and a hard disk but also a transmission medium for temporarilystoring data like a network.

Moreover, the embodiment explained about differential waveform. However,ordinary signal waveform may also be used.

As described above, according to the present invention, it is possibleto easily perform the random-pattern analysis and skew analysis ofhigh-frequency differential waveforms or ordinary signal waveforms.

Moreover, it is possible to immediately return a good/bad determinationresult to high-frequency circuit design.

Furthermore, it is possible to increase the accuracy of the waveformanalysis.

In addition, it is possible to increase the accuracy of the good/baddetermination of the eye-patterns.

What is more, it is also possible to decrease the effects of phaseshifts and distortion and to obtain eye-patterns of which their good orbad can be determined.

Moreover, the good/bad determination can be performed with eye-patternshaving little effects of phase shifts and distortion and the accuracy ofthe good/bad determination can be increased.

Although the invention has been described with respect to a specificembodiment for a complete and clear disclosure, the appended claims arenot to be thus limited but are to be construed as embodying allmodifications and alternative constructions that may occur to oneskilled in the art which fairly fall within the basic teaching hereinset forth.

1. An apparatus for signal-waveform simulation, comprising: a modelgeneration unit which generates a signal-analysis simulation model inaccordance with high-frequency-circuit design information; arandom-pattern analysis unit which generates and analyzes a dummyrandom-pattern waveform for transmitting the signal-analysis simulationmodel and a differential waveform corresponding to the dummyrandom-pattern waveform in accordance with a command including the bitinformation of a random-pattern waveform; a skew analysis unit whichskews the random-pattern waveform or the differential waveform inaccordance with a preset skew width; an eye-pattern analysis unit whichgenerates an eye-pattern waveform by superimposing waveforms obtained byframe-dividing the random-pattern waveform or the differential waveform;and a determination unit which determines qualities of the eye-patternwaveform in accordance with a reference eye pattern and based on an areaof an eye, wherein when it is determined that an eye portion of theeye-pattern waveform enters the reference eye pattern, the determinationunit displays waveforms corresponding to an error bit and a plurality ofbits before and after the error bit associated with the eye-patternwaveform.
 2. The apparatus according to claim 1, further comprising: ajitter analysis unit which generates jitter in the random-patternwaveform in accordance with a preset jitter addition value.
 3. A methodof signal-waveform simulation, comprising the steps of: generating asignal-analysis simulation model in accordance withhigh-frequency-circuit design information; generating a dummyrandom-pattern waveform for transmitting the signal-analysis simulationmodel and a differential waveform corresponding to the dummyrandom-pattern waveform in accordance with a command including the bitinformation of a random-pattern waveform and analyzing them; and skewingthe random-pattern waveform or the differential waveform in accordancewith a preset skew width; generating an eye-pattern waveform bysuperimposing waveforms obtained by frame-dividing the random-patternwaveform or the differential waveform; determining qualities of theeye-pattern waveform in accordance with a reference eye pattern andbased on an area of an eye; and displaying waveforms corresponding to anerror bit and a plurality of bits before and after the error bitassociated with the eye-pattern waveform when it is determined that aneye portion of the eye-pattern waveform enters the reference eyepattern.
 4. A computer readable medium for storing instructions, whichwhen executed on a computer, causes the computer to perform a methodcomprising: generating a signal-analysis simulation model in accordancewith high-frequency-circuit design information; generating a dummyrandom-pattern waveform for transmitting the signal-analysis simulationmodel and a differential waveform corresponding to the dummyrandom-pattern waveform in accordance with a command including the bitinformation of a random-pattern waveform and analyzing them; skewing therandom-pattern waveform or the differential waveform in accordance witha preset skew width; generating an eye-pattern waveform by superimposingwaveforms obtained by frame-dividing the random-pattern waveform or thedifferential waveform; determining qualities of the eye-pattern waveformin accordance with a reference eye pattern and based on an area of aneye; and displaying waveforms corresponding to an error bit and aplurality of bits before and after the error bit associated with theeye-pattern waveform when it is determined that an eye portion of theeye-pattern waveform enters the reference eye pattern.
 5. An apparatusfor signal-waveform simulation, comprising: a model generation unitwhich generates a signal-analysis simulation model in accordance withhigh-frequency-circuit design information; a random-pattern analysisunit which generates and analyzes a dummy random-pattern waveform fortransmitting the signal-analysis simulation model and a differentialwaveform corresponding to the dummy random-pattern waveform inaccordance with a command including the bit information of arandom-pattern waveform; a setting unit which sets a region to beexcluded from a range to be analyzed in the random-pattern waveform orthe differential waveform; an eye-pattern analysis unit which generatesan eye-pattern waveform by superimposing waveforms obtained byframe-dividing the random-pattern waveform or the differential waveform;and a determination unit which determines qualities of the eye-patternwaveform in accordance with a reference eye pattern and based on an areaof an eye, wherein when it is determined that an eye portion of theeye-pattern waveform enters the reference eye pattern, the determinationunit displays waveforms corresponding to an error bit and a plurality ofbits before and after the error bit associated with the eye-patternwaveform.
 6. An apparatus for signal-waveform simulation, comprising: amodel generation unit which generates a signal-analysis simulation modelin accordance with high-frequency-circuit design information; arandom-pattern analysis unit which generates and analyzes a dummyrandom-pattern waveform for transmitting the signal-analysis simulationmodel and a differential waveform corresponding to the dummyrandom-pattern waveform in accordance with a command including the bitinformation of a random-pattern waveform; an eye-pattern analysis unitwhich generates an eye-pattern waveform by superimposing waveformsobtained by frame-dividing the random-pattern waveform or thedifferential waveform by a division width that includes a waveform ofone bit and is of one data width or wider; a determination unit whichdetermines qualities of the eye-pattern waveform in accordance with areference eye pattern and based on an area of an eye, wherein when it isdetermined that an eye portion of the eye-pattern waveform enters thereference eye pattern, the determination unit displays waveformscorresponding to an error bit and a plurality of bits before and afterthe error bit associated with the eye-pattern waveform.
 7. A computerprogram containing instructions which when executed on a computer causesthe computer to realize the units of: a model generation unit whichgenerates a signal-analysis simulation model in accordance withhigh-frequency-circuit design information; a random-pattern analysisunit which generates and analyzes a dummy random-pattern waveform fortransmitting the signal-analysis simulation model and a differentialwaveform corresponding to the dummy random-pattern waveform inaccordance with a command including the bit information of arandom-pattern waveform; a skew analysis unit which skews therandom-pattern waveform or the differential waveform in accordance witha preset skew width; an eye-pattern analysis unit which generates aneye-pattern waveform by superimposing waveforms obtained byframe-dividing the random-pattern waveform or the differential waveform;and a determination unit which determines qualities of the eye-patternwaveform in accordance with a reference eye pattern and based on an areaof an eye, wherein when it is determined that an eye portion of theeye-pattern waveform enters the reference eye pattern, the determinationunit displays waveforms corresponding to an error bit and a plurality ofbits before and after the error bit associated with the eye-patternwaveform.
 8. A computer program containing instructions which whenexecuted on a computer causes the computer to realize the units of: amodel generation unit which generates a signal-analysis simulation modelin accordance with high-frequency-circuit design information; arandom-pattern analysis unit which generates and analyzes a dummyrandom-pattern waveform for transmitting the signal-analysis simulationmodel and a differential waveform corresponding to the dummyrandom-pattern waveform in accordance with a command including the bitinformation of a random-pattern waveform; a setting unit which sets aregion to be excluded from a range to be analyzed in the random-patternwaveform or the differential waveform; an eye-pattern analysis unitwhich generates an eye-pattern waveform by superimposing waveformsobtained by frame-dividing the random-pattern waveform or thedifferential waveform; and a determination unit which determinesqualities of the eye-pattern waveform in accordance with a reference eyepattern and based on an area of an eye, wherein when it is determinedthat an eye portion of the eye-pattern waveform enters the reference eyepattern, the determination unit displays waveforms corresponding to anerror bit and a plurality of bits before and after the error bitassociated with the eye-pattern waveform.
 9. A computer programcontaining instructions which when executed on a computer causes thecomputer to realize the units of: a model generation unit whichgenerates a signal-analysis simulation model in accordance withhigh-frequency-circuit design information; a random-pattern analysisunit which generates and analyzes a dummy random-pattern waveform fortransmitting the signal-analysis simulation model and a differentialwaveform corresponding to the dummy random-pattern waveform inaccordance with a command including the bit information of arandom-pattern waveform; a setting unit which sets a region to beexcluded from a range to be analyzed in the random-pattern waveform orthe differential waveform; an eye-pattern analysis unit which generatesan eye-pattern waveform by superimposing waveforms obtained byframe-dividing the random-pattern waveform or the differential waveformby a division width that includes a waveform of one bit and is of onedata width or wider; an eye-pattern analysis unit which generates aneye-pattern waveform by superimposing waveforms obtained byframe-dividing the random-pattern waveform or the differential waveform;and a determination unit which determines qualities of the eye-patternwaveform in accordance with a reference eye pattern and based on an areaof an eye, wherein when it is determined that an eye portion of theeye-pattern waveform enters the reference eye pattern, the determinationunit displays waveforms corresponding to an error bit and a plurality ofbits before and after the error bit associated with the eye-patternwaveform.
 10. An apparatus, comprising: a model generation unit whichgenerates a signal-analysis simulation model in accordance withhigh-frequency-circuit design information; a random-pattern analysisunit which generates and analyzes a dummy random-pattern waveform fortransmitting the signal-analysis simulation model and a differentialwaveform corresponding to the dummy random-pattern waveform inaccordance with a command including the bit information of arandom-pattern waveform; a skew analysis unit which skews therandom-pattern waveform or the differential waveform in accordance witha preset skew width; an eye-pattern analysis unit which generates aneye-pattern waveform by superimposing waveforms obtained byframe-dividing the random-pattern waveform or the differential waveform;and means for determining qualities of the eye-pattern waveform inaccordance with a reference eye pattern and based on an area of an eye,wherein when it is determined that an eye portion of the eye-patternwaveform enters the reference eye pattern, waveforms are displayedcorresponding to an error bit and a plurality of bits before and afterthe error bit associated with the eye-pattern waveform.